On Oracle Database, DBAs can check broken job for Oracle Job (dbms_job) at *_JOBS.BROKEN column. Anyway, DBAs have changed from DBMS_JOB to DBMS_SCHEDULER. So, I was curious How to check broken job for Oracle Scheduler (DBMS_SCHEDULER)?
After found out... DBAs can check on *_SCHEDULER_JOBS.STATE
|Current state of the job:|
When does Oracle Scheduler change STATE to be BROKEN?
This post is more of a note for myself and might be helpful to few other. Assuming db is 11gR2 and baselines/spm is used. When a new query is introduced in db, it might be that it runs with the good plan, but sometimes it picks up wrong plan. It could be that Index Range [&hellip
At March I will be presenting my very successful seminar “Mastering Backup and Recovery” in some countries of Latin America for the very first time. Thank you Panama, Chile and Brazil OUGs for inviting me to your amazing countries! Please, use the following links for registration and also to find more information about the seminar: […]
Hi All, On February 4, 2014 at 9:30 am PT I will be talking on the next OTN Virtual Developer Day about Oracle VM and Oracle Database. Come and discover the answers for the following questions: Does an Oracle Database perform well on a virtualized environment? What virtualization technology is more stable and […]
A new version of the XPLAN_ASH tool (detailed analysis of a single SQL statement execution) is available for download. The previous post
includes links to video tutorials explaining what the tool is about.As usual the latest version can be downloaded here.
The new version comes with numerous improvements and (more...)
When the optimizer has to estimate the data volume (the BYTES
column in the plan output), it usually bases this information on the column statistics
, if applicable and available (think of complex expressions).However, whenever there is a VIEW operator
in an execution plan, that represents an unmerged view, the optimizer obviously "loses" this information and starts applying defaults that are based on the column definition
.Depending on the actual content of the columns (more...)
Yesterday I was creating a new Oracle 184.108.40.206 database from a copy of datafiles and archivelogs taken from our standby. I was sure to include archivelogs from just prior to well after the span of the datafile backup time. I had created a new controlfile, gotten everything (more...)
Note: The following is based on testing with 220.127.116.11 (I believe same issue exists within other Oracle versions).
I recently worked on an interesting problem relating to the “enq: TX – contention” wait event. There are a number of reasons for the wait but the most common (more...)
The TIMESTAMP WITH TIME ZONE data type that got introduced a long time ago is known for some oddities, for example Tony Hasler has a nice summary of some of them here
.Here is another oddity that shows up when trying to aggregate on such a data type. Have a look at the following simple example:
create table t
rownum as id
, date '2000-01-01' + rownum - 1 as some_date
, cast(date (more...)
A new major release (version 3.0) of my XPLAN_ASH tool is available for download.You can download the latest version here.
In addition to many changes to the way the information is presented and many other smaller changes to functionality there is one major new feature: XPLAN_ASH now also supports S-ASH
, the free ASH implementation.
If you run XPLAN_ASH in a S-ASH repository owner schema, it will automatically detect that and adjust accordingly. (more...)
When using Locally Managed Tablespaces
(LMT) with variable, system managed extent sizes (AUTOALLOCATE
) and data files residing in ASM
the Allocation Unit (AU)
size can make a significant difference to the algorithm that searches for free extents.The corresponding free extent search algorithm when searching for free extents >= the AU size
seems to only search for free extents on AU boundaries
in order to avoid I/O splitting
.Furthermore the algorithm seems to (more...)
My site uses a 3rd party SQL monitoring tool which collects data based on the Oracle view v$sqlstats. The tool collects data for all sql statements which have been executed since the previous collection using the last_active_time column. A few months ago we noticed (after an upgrade to 11g) we (more...)
In the previous post
I've demonstrated an unexpected Nested Loop Join caused by an extreme data distribution. Although unexpected at first sight, the performance of the execution plan selected by the optimizer is decent - provided the estimates are in the right ballpark.Here is another case of an unexpected execution plan, this time about Merge Joins
In order to appreciate why the execution plan encountered is unexpected, first a quick summary about (more...)
Recently I came across some interesting edge cases regarding the costing of joins. They all have in common that they result in (at first sight) unexpected execution plans, but only some of them are actual threats to performance.
The first one is about outer joins
with an extreme data distribution. Consider the following data setup:
create table t1
rownum as id
, rpad('x', 100) as filler
, case when rownum > (more...)
I just stumbled upon this bug reference on My Oracle Support:
Bug 13262857 Enh: provide some control over DBMS_STATS index clustering factor computation
This enhancement was long due. Previously, when computing the clustering factor during gathering statistics, the value was incremented, whenever the row was not found in the same block as the previous row. Now, it is finally possible to determine how many blocks should be considered when computing clustering factor. The patch delivers an improved DBMS_STATS package body that can be used to set preferences with value TABLE_CACHED_BLOCKS.
The flaw in the over-simplistic and pessimistic original computation was (more...)
Oracle 10g introduced the QB_NAME
hint that can come handy in case hints need to be applied to more complex statements, in particular when possibly multiple layers of views / subqueries are involved.Jonathan Lewis has a older blog post
that describes more details.Just in case you wonder why sometimes apparently the QB_NAME
hint - along with all other hints that refer to the assigned query block name - seems to be ignored: One (more...)
Here is an interesting limitation to Exadata Smart Scans
- if more than 254 columns
from a table (not HCC compressed, more on that in moment) need to be projected, Smart Scans for that particular segment will be disabled
and Exadata will fall back to conventional I/O. This means that the number of columns in the projection clause can make a significant difference
to performance, since only Smart Scans allow taking advantage of offloading
Oracle Flashback database and restore points enables us to rewind the database back in time to correct any problems caused by logical data corruption or user errors and it doesn’t require any restoration of backup. There are 2 types of restoration points – 1. Normal Restore Point –> assigns a restore point name to an